The human auditory system can detect quiet sounds while tolerating sounds a million times more intense, and it can discriminate time differences of a couple of microseconds. Even more amazing is the ability of the human auditory system to perform auditory scene analysis, whereby the auditory system computationally separates complex signals impinging on the ears into component sounds representing the outputs of different sound sources in the environment. However, with hearing loss the auditory source separation capability of the system breaks down, resulting in an inability to understand speech in noise. One manifestation of this situation is known as the “cocktail party problem” in which a hearing impaired person has difficulty understanding speech in a noisy room.
There have been several recent advances in understanding the neurophysiological basis of hearing impairment. The insight that damage to the hair cells within the inner ear alters the auditory system must have a profound effect on the design of hearing-aid systems to combat sensorineural hearing loss. However, current hearing-aid technology does not make full use of this information. Up until the mid 1980's, the mechanisms underlying the more prevalent types of impairment due to hair cell loss were not well understood. This led to a group of ad-hoc algorithms, largely based on the discerned symptoms (spectrally shaped sensitivity loss, identification in noise problems) as opposed to the mechanisms underlying the symptoms. Hearing-aid algorithms are still based on conductive impairment, which can arise after ossicle damage or an ear drum puncture, and can largely be overcome with frequency-shaped linear amplification. The types of impairment associated with sensorineural hearing loss (i.e. Inner Hair Cell (IHC) and Outer Hair Cell (OHC) damage) requires a new suite of algorithms. The loss of these hair cells produces symptoms such as elevated thresholds, loss of frequency selectivity, loss of contrast enhancement, and loss of temporal discrimination. This invention emphasizes a new suite of algorithms to deal specifically with sensorineural impairment.